Induction heating furnace and method of heating



A. w. LILLIENBERG ETAL 2,843,712

INDUCTION HEATING FURNACE AND METHOD OF HEATING Filed Oct. 3. 1956 Q 2Sheets-Sheet l INVEN TORS A TTOR/VEKS.

y 15, 1958 A. w.- LILLIENBERG ETAL 2,843,712

INDUCTION HEATING FURNACE AND METHOD OF" HEATING Filed 001;. a, 1956 r 2Sheets-Sheet 2 ATTORNEYS.

United States Patent O INDUCTION HEATING FURNACE AND METHOD OF HEATINGAugust W. Lillienberg, Chicago, Ill., and George V. Harris, Racine,Wis., assignors to Lindberg Engineering Company, Chicago, 111., acorporation of Illinois Application October 3, 1956, Serial No. 613,721

12 Claims. (Cl. 21910.41)

of furnace comprises a hollow heating chamber into which a charge of thework materials to be heated is placed for a desired period of time afterwhich the treated materials are removed and another charge of workmaterials is placed in the furnace for treatment.

Another conventional type of furnace comprises an elongated hollowheating chamber through which the work materials are conveyed byautomatic or manual conveyor means. In this type of furnace the workmaterials may be passed continuously through the furnace for heatmg.

The first type of furnace above mentioned has the disadvantage of beingcapable of handling only relatively small charges of work material as itdoes not function continuously. The second type of furnace mentionedabove, while adapted for continuous heating operation, has thedisadvantage of requiring relatively long heating chambers and,therefore, such furnaces are expensive both from the viewpoint ofconstruction costs and from the amount of floor space required.

In addition to the above, such prior art types of heating furnacesfrequently require generally complex control means for maintaining adesired atmosphere within the furnace since this problem is aggravatedby the relatively large inherent leakage therein. Since atmospheric gasis rather expensive, this serves to add to the cost of operation of suchfurnaces.

Accordingly, it is a general object of this invention to provide animproved electric heating furnace and method of heating work materials.

It is another object of this invention to provide an improved electricheating furnace of relatively compact construction having a capacityequivalent to the capacity of conventional furnaces of substantiallygreater size.

It is still another object of this invention to provide a continuouslyoperating electric heating furnace in which the need for a complex andexpensive separate conveyor means for the work materials is eliminated.

It is a further object of this invention to provide an improved electricheating furnace in which the work materials are advanced through thefurnace by the cyclical movement of the heating chamber.

It is a still further object of this invention to provide an improvedelectric heating furnace in which the heating chamber is physically andelectrically isolated from the source of electrical energy.

According to one feature of the invention both the heating chamber andthe work therein are heated by induced electric current.

It is a still further object of this invention to provide .an improvedelectric heating furnace which is character- Patented July 15,1958

. 2 ized by its compact construction, its efiiciency and its economy ofoperation.

In accordance with the features of a specific illustrative embodiment ofthis invention the improved electric heating furnace comprises aring-shaped hollow outer shell which preferably is formed of anon-magnetic material, such as aluminum or the like. A smallerring-shaped hollow member defining an annular heating chamber ispositioned within the outer shell and advantageously is thermallyinsulated therefrom.

This istattained by lining the lower interior portion of the outer shellwith a heat resistant refractory, such as brickwork or ceramic, uponwhich the annular heating chamber is supported. The remaining spacebetween the outer shell interior and the annular heating chamber isfilled with a heat insulating material and the heating chamber is afixedto the refractory, as by bolts and the like, to maintain the heatingchamber securely in position.

The heating chamber is provided with a loading channel, such as atubular member which extends through the outer shell and is connectedwith an opening in the heating chamber for enabling work materials to beinserted in the latter. The heating chamber also is provided with adischarge channel, which may be a tubular member extending from anopening in the lower portion of the heating chamber through the outershell, to enable the treated Work material to be discharged into aquenching bath or other receivingmeans.

In accordance with a primary feature of this invention, the ring-shapedheating structure which comprises the outer shell and heating chamber ismounted upon bearings to the end that the heating structure may becyclically oscillated about its vertical axis in a relatively easymanner upon the bearings. This may be attained by any suitable actuatingmechanism linked to the outer shell, which mechanism may take the formof a hydraulic cylinder, an air cylinder or any suitable electrical ormechanical device capable of reciprocating the heating structure backand forth at a controllable rate. Thus, it will be appreciated that thework materials inserted into the heating chamber through the loadingchannel are caused to advance through the chamber towards the dischargechannel as the result of the jogging motion provided by thereciprocation of the heating structure, the rate of advance and, hencethe heating cycle of the work materials, being controlled by the rate ofreciprocation.

Heating of the work material is attained by means of a transformer coreand primary winding which is operatively associated with the outershell. In accordance with one embodiment of this invention, thetransformer core completely encloses a portion of the outer shell andthe primary coil is wound upon one leg thereof so as to be inductivelycoupled with the heating chamber within the outer shell when electricalenergy is supplied thereto. Thus, the heating chamber serves as thesecondary winding of the transformer and when electrical energy issupplied to the transformer the heating chamber is heated to heat thework material as it is advanced through the heating chamber duringreciprocation in the manner explained above.

It will be appreciated from the viewpoint of efficient operation that itis desirable to heat only the heating chamber within the outer shell. Tothis end the outer shell is separated at a portion thereof and the endsare joined by means of an electrical insulating material such that thereis no complete electrical path around the outer shell.

In the operation of the heating furnace, Work material is continuouslysupplied to the heating chamber through the loading channel and isadvanced around the chamber towards thedischarge channel as aresult ofthe reciprocation of the heating structure. The diameter of thering-shaped heating chamber is chosen so the work material is heated fora desired period of time before it is discharged through the dischargechannel and in accordance with available floor space. It will beunderstood that a heating area equivalent to that of a relativelylengthy heating furnace of the prior art elongated type may be attainedwith a comparatively small diameter ring-shaped heating chamber. Thus,savings in both floor space and in construction costs are effected by aheating furnace constructed in accordance with the invention.

'In another preferred embodiment of the invention, the heating area ofthe heating chamber may be increased without any corresponding increasein the horizontal dimensions of the heating furnace by providing aspiral type of heating chamber within the outer shell. Thus, the heatingchamber may comprise not one but a plurality of turns within the outershell. A loading channel is provided at the uppermost turn and adischarge channel is provided at the lowermost turn to the end that thework materials are advanced from the top to the bottom of the spiralduring reciprocation. As it is necessary that the heating chambercomprise a completely closed electrical path in order to serve as thesecondary coil of the transformer, the loading and discharge ends of theheating chamber are electrically connected as by means of a strap or thelike.

It will be appreciated that since the heating chamber is substantiallycompletely enclosed in either of the abovedescribed embodiments,confinement of atmospheric gases therein is greatly facilitated. Thus,an atmospheric inlet channel, such as a tubular member, may be providedin communication with the heating chamber and extending through theouter shell to enable the atmospheric gases to be supplied to theheating chamber. This also serves to provide increased economy ofoperation of the heating furnace.

It further will be appreciated that the heating chamber may be formedwith a variable resistance throughout its length to provide control ofheat release therein. Thus, the cross section of the heating chamber maybe smaller at the points where increased heat is required, such as atthe loading and discharge ends, and the cross section may be reducedthroughout the remainder of the heating chamber to decrease the heatingtemperature thereat. Additionally, control of heat release around the360 of the heating chamber may be provided by means of the electricalon-off control associated with the transformer primary winding.

The above and other features of novelty which characterize the inventionare pointed out with particularity in the claims appended to and forminga part of this specification. For a better understanding of thisinvention, however, its advantages and the specific objects attained byits use, reference is had to the accompanying drawing and descriptivematerial in which is shown and described several illustrativeembodiments of the invention.

In the drawings:

Figure 1 is a perspective view of an electric heating furnace embodyingthe invention;

Figure 2 is a top plan view of the furnace;

Figure 3 is a partial section on the line 33 of Fig ure 2;

Figure 4 is a vertical section on the line 44 of Figure 2;

Figure 5 is a section similar to Figure 4 of an alternative constructionembodying the invention; and

Figure 6 is a perspective view of the heating chamber of the furnaceshown in Figure 5.

The furnace, as shown in Figures 1 to 4, comprises a generally annularor ring-shaped body, indicated generally at 10, through which thematerial to be heated is passed. The ring-shaped body 10 is movablysupported on a supporting framework including legs 11 carryinghearingelements, such as, rollers 12, which support the body 10. Theframe may be suitably mounted on a floor or the like and the legs areinsulated from each other as by an insulating supporting plate 13 whichholds the legs in proper spaced relationship.

The annular ring-shaped body 10, as best seen in Figures 3 and 4, isformed by an outer metallic shell 14 formed of any suitable metal, suchas light gauge steel, aluminum, or the like. To prevent induced currentsin the shell 14 it is electrically interrupted by insulating strips 15,as best seen in Figures 2 and 3, so that no current can fiow around theshell.

An annular ring-shaped heating chamber 16, which may be formed of a heatresistant electrically conductive material such as steel, is mountedwithin the shell 14 and is heat insulated therefrom. For this purpose,as shown, the chamber 16 may rest upon refractory material 17, such asbrickwork or the like, and the space at the sides of and above theheating chamber may be filled with a heat insulating material 18 of anydesired type. The insulating material 18 may take the form of a pouredor cast refractory or may be loose refractory insulating material asdesired.

Work to be heated is fed into the heating chamber 16 through an inletconduit 19, as best seen in Figure 3, which extends through the outershell 14 and the insulating material 18 into the annular heating chamber16. As shown, the conduit 19 is fitted through an enlarged opening inthe outer shell 14 and is spaced from the walls of the opening to beelectrically insulated from the shell. The work is discharged from theheating chamber 16 through a similar conduit 21 extending downwardlyfrom the heating chamber 16 through the heat insulating material and theouter shell. In operation, work is fed into the inlet conduit 19 andtravels around the heating chamber to be discharged after heatingthrough the conduit 21 into a suitable quenching tank or the like.

To heat the work an electrical primary unit is provided to induce theflow of heating current in the heating chamber 16 and the work therein.As shown, the primary unit comprises a rectangular core 22 looped aroundthe annular body 10 and carrying a primary winding 23 which, preferably,lies within the body 10. The core 22 is supported by plates 24 attachedto the insulating disc 13. When the winding 23 is energized byalternating current and, preferably, by high frequency current asecondary heating current will be induced in the annular heating chamber16 to heat the chamber and by conduction to heat the work therein. Asthe work in the chamber passes through the magnetic field created by thewinding 23, secondary current will also be induced directly in the workitself to augment the heating effect. In this way the work is heated tothe desired temperature as it passes through the heating chamber, thedesired degree of heating being achieved by regulating the frequency andvoltage of the primary current and the time of retention of the work inthe heating chamber.

In many instances it may be desirable to vary the heating effect on thework as it travels through the heating chamber. For this purpose, it iscontemplated that the cross-sectional area of the heating chamber wallsmay be varied to produce a greater intensity of current at points wherethe cross-sectional area of the walls is reduced so that the heatdistribution may be effectively regulated. For example, it may bedesirable to provide a high temperature adjacent the inlet opening tobring the work up to treating temperature rapidly.

The work is advanced through the heating chamber according to thepresent invention by reciprocating or oscillating the heating chamber toadvance the work therethrough. Any desired type of reciprocating oroscillating means may be employed such as, for example, a fluid motor,as shown in Figure 2. In this construction a cylinder 25 is pivoted atone end to the supporting plates 24, or if preferred directly to thecore 22 itself, and contains a piston whose piston rod 26 is pivotallyconnected to a bracket 27 on the annular body 10. Fluid may be suppliedalternately to opposite ends of the cylinder through suitable automaticvalve means (not shown) to cause the body to oscillate on the supportingrollers 12. It will be understood that the body 10 may advancerelatively slowly in the direction of travel of the work from the inletto the discharge conduit so that the work will be carried around in theheating chamber and may be returned rapidly in the opposite direction sothat the work will not return with it. The rate of travel of the workthrough the heating chamber may be adjusted by adjusting the rate ofoscillation of the body to provide the required retention time of thework in the chamber.

The furnace of the present invention adapts itself readily to treatmentof the work in an atmosphere gas. For this purpose a conduit 28 mayextend through the shell and insulating material into the heatingchamber and may be connected through a flexible hose to a gas generator.Since the chamber is closed except for the inlet and outlet conduits,there will be a relatively small consumption of atmosphere gas and thechamber may be maintained properly filled at all times. The temperatureof the chamber may be indicated by means of a thermocouple 29 or thelike extending through the shell into contact with the chamber andcarrying a suitable indicating instrument at its upper end or connected.through flexible leads to a remote indicating instrument.

In operation of the furnace as shown in Figures 1 to 4, the primarywinding 23 may be energized and the annular body 10 may be oscillated atthe desired rate. Work pieces to be treated are introduced into thechamber 16 through the inlet conduit 19 and are caused to travel aroundin the heating chamber in a counterclockwise direction, as seen inFigure 2, to the outlet conduit. During their passage through theheating chamber, the work pieces are heated by conduction from the Wallsof the heating chamber and also by induced secondary current directly inthe work pieces themselves. Thus, the work pieces may be heated to anydesired temperature and maintained at the desired temperature for therequired length of time to effect the desired heat treatment.

Since the heating chamber is annular, it provides a relatively long pathof travel for the work in a highly confined compact space. Furthermore,the annular construction of the heating chamber provides an effectivesecondary loop for conduction of secondary heating current to effectheating.

Where still greater retention time is desired, or greater compactness isrequired, the construction shown in Figures 5 and 6 may be employed. Thefurnace shown in these figures comprises an annular body, indicatedgenerally at 30, which is similar to the annular body 10 but may bedeeper. This body includes a shell 31 formed of metal and interrupted atat least one point in its periphery so that current cannot flowtherethrough. A spiral heating chamber 32 is mounted within the shell 31and is spaced therefrom by heat insulating material 33 to support thespiral chamber and to insulate it from the shell.

The chamber 32 may be formed with any desired number of turns in theform of a helix, as shown, or if preferred as a flat spiral. Asillustrated in Figure 6, the heating chamber comprises two completeturns With one end extending upwardly to define an inlet conduit 34 toproject through the shell 31 and the opposite end turned downwardly todefine an outlet conduit 35 also projecting through the shell 31. Inorder that the spiral chamber may define a complete closed secondaryloop, a conducting strap 36 is connected directly between the inlet andoutlet portions of the body so that current can flow through thecomplete body.

Secondary current is induced in the spiral body and in the work thereinby means of a primary unit including a core 37 looped around the body30, as shown in 6 Figure 5, and carrying a primary winding 38,preferably within the body.

This construction functions in exactly the same manner as theconstruction of Figures 1 to 4. In operation, the body is oscillated orreciprocated in the same manner as the body 10 of Figures 1 to 4 tocause the work pieces to travel around the spiral from the inlet to thedischarge end. During the travel, the work pieces are heated byconduction from the body itself due to induced secondary current thereinand by induced currents directly in the work pieces themselves. With theconstruction of Figure 5 an extremely great length of chamber can beprovided in a very compact space so that long retention time and a highdegree of heating can be achieved.

While two embodiments of the invention have been shown and described indetail, it will be understood that these are illustrative only and arenot to be taken as a definition of the scope of the invention, referencebeing had for this purpose to the appended claims.

We claim:

1. An electric heating furnace comprising a movable heating structureincluding a substantially ring-shaped hollow outer shell, a smallerring-shaped hollow heating chamber enclosed within said outer shell andthermally insulated therefrom, a loading channel extending through saidouter shell and communicating with the interior of said heating chamberfor enabling work material to be placed within the latter, a dischargechannel extending through said outer shell and communicating with theinterior of said chamber to enable heated work material to be dischargedfrom the latter, bearing means supporting said movable heatingstructure, actuating means linked to said movable heating structure forcausing the latter to be reciprocated in said bearing means to advancethe work material in said chamber from the loading channel towards thedischarge channel, and a stationary core having a transformer primaryWinding wound thereon in operative association with said heatingstructure and adapted when energized to cause the work material withinsaid heating chamber to be heated.

2. An electric heating furnace in accordance with claim l furthercomprising an atmosphere inlet channel extending through said outershell and communicating with the interior of said heating chamber forsupplying atmospheric gases thereto.

3. An electric heating furnace in accordance with claim 1 wherein saidring-shaped outer shell is formed with an insulating segment at oneportion thereof to provide a discontinuity in the electric circuitaround said outer shell.

4. An electric heating furnace comprising a movable hollow memberdefining a heat treating chamber, a loading channel communicating withthe interior of said chamber for enabling work material to be placedwithin the latter, a discharge channel communicating with the interiorof said channel to enable treated work material to be discharged fromthe latter, bearing means supporting said heating chamber, actuatingmeans including an energizable cylinder having a piston connected tosaid movable hollow member for causing the latter to be reciprocated insaid bearing means for advancing the work material in said chamber fromthe loading channel towards the discharge channel, and a stationary corehaving a transformer primary coil wound thereon inductively coupled tosaid heating chamber and adapted when energized to cause said heatingchamber and the work material therein to be heated.

5. An electric heating furnace comprising a hollow outer shell, aheating chamber positioned within said outer shell and thermallyinsulated therefrom, means for enabling work material to be loaded intoand discharged from said heating chamber, actuating means linked to saidouter shell for causing said heating chamber to be reciprocated foradvancing the work material therein, and transformer primary meansinductively coupled -to 7 said heating chamber and adapted whenenergized to cause said chamber and the work material therein to beheated. Y

6. An electric hollow heating furnace comprising a heating chamberhaving inlet and outlet ends for Work material to be heated, means forsupporting said heating chamber so as to enable movement thereof,actuating means operatively associated with said heating chamber forcyclically moving the same for causing said work material to be advancedin discrete steps from said inlet to said outlet end, and transformerprimary means including a core and an electrical conductor wound thereoninductively coupled to said heating chamber for causing the workmaterial to be heated as it is advancedthrough said heating chamberduring said movement.

7. An electric heating furnace in-accordance with claim 6 furthercomprising an inlet channel extending through a wall of said hollowchamber and communicating with the interior thereof for controlling theatmosphere therein.

8. An electric heating furnace comprising a hollow body defining ahousing, bearing means supporting said body, actuating means linked tosaid body for causing the latter to be cyclically actuated in saidbearing means, a hollow coiled member adapted for the passage of workmaterial to be heated therethrough positioned within said hollow body,said coiled member comprising a plurality of turns and having a loadinginlet at the upper portion of said housing and a discharge outlet at thelower portion of said housing, means electrically connecting said coiledmember at its inlet and outlet ends to form a closed electrical pathwhereby said coiled member is adapted to serve as a transformersecondary, and a transformer primary operatively associated with saidhousing, said transformer primary including a stationary core and aprimary coil inductively coupled to said coiled member for heating thecoiled member and the work material during cyclical actuation of saidbody, whereby the work material is advanced from said loading inlettowards said discharge outlet during heating.

9. An electric heating furnace comprising a hollow body defining ahousing, actuating means linked to said body for causing the latter tobe reciprocated about a vertical axis, a hollow coiled member comprisinga plurality of turns and adapted for the passage of work material to beheated therethrough positioned within said hollow body, meanselectrically connecting turns of said coiled member to form a closedelectrical path for enabling said coiled member to serve .as atransformer secondary, and a transformer primary operatively associatedwith said body, said transformer primary including a stationary core anda primary coil inductively coupled to said coiled member for heating thecoiled member and the work material during reciprocation of said body.

10. An electric heating furnace in accordance with claim 9 wherein saidhollow coiled member is substantially closed and further comprising anatmosphere inlet member communicating with the interior of said coiledmember for enabling control of the atmosphere therein.

11. The method of heating work material in an electric furnace whichcomprises the steps of providing in the furnace a closed heating chamberhaving loading and discharge openings for the passage of work materialto be heated therethrough, reciprocating said heating chamber to causesaid work material to be advanced from the loading opening of thechamber to the discharge opening of the chamber, and inducing electricheating current in said chamber and the work material therein duringreciprocation of the chamber.

12. The method of heating work material in an electric furnace whichcomprises the steps of providing in the furnace a plural-turn hollowcoiled heating chamber having loading and discharge openings at itsupper and lower ends, respectively, for the passage of work material tobe heated therethrough, reciprocating said heating chamber to cause saidwork material to be advanced from the loading end of the heating chamberto the discharge end of the heating chamber, electrically connecting theends of the heating chamber, and inducting electric heating current inthe heating chamber.

References Cited in the file of this patent UNITED STATES PATENTS1,821,530 Spire Sept. 1, 1931 2,555,450 Lee June 5, 1951 2,616,022Arnaud Oct. 28, 1952 2,729,731 Kleinpeter Jan. 3, 1956

